Grit-mediated frictional ignition of a polymer-bonded explosive during oblique impacts: Probability calculations for safety engineering

Transportation, handling, vibrations can lead to dynamic loadings requiring the characterization of the safety of plastic‐bonded explosives (PBX). One of the addressed situations is the fall of explosive on a surface. Knowing that initiation can occur at a lower height during a vertical fall of a projectile on an inclined target than on a horizontal one, devices were developed to determine the critical thresholds. In this paper, data obtained on four HMX and/or TATB‐based PBXs using pendulum drop configurations are detailed. Two analytical models are compared to estimate the heat released by friction at the interface. The model proposed in this paper yields the better agreement with data, and with finite element numerical simulations of the oblique impact on a given PBX. Lastly, the mechanical dissipation at the interface is estimated using this model and the simulations. This paper confirms that PBX/target friction cannot be the heating mechanism leading to initiation during oblique impacts.

Section: Introductionmentioning

confidence: 77%

Section: Finite Element Evaluation Of the Heatingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Oblique Impacts and Friction of HMX and/or TATB‐based PBXs

Picart

Junqua-Moullet

2017

“…The inference drawn there was that the well-understood influence of high melting-temperature grit on the surface was the cause. However, experiments with gritted Steven tests have not been performed, and skid test experiments on clean surfaces produced no ignition [42]. From these test results, we cannot infer for our model a quantitative increase in sensitivity to shear ignition caused by grit.…”

Section: Shear Ignitionmentioning

confidence: 89%

A Computer Model to Study the Response of Energetic Materials to a Range of Dynamic Loads

Reaugh

White

Curtis

et al. 2018

Over the past decade we developed a model to enable computer simulation of the mechanical and subsequent energetic response of explosives and propellants to mechanical insults such as impacts, perforations, drops, and falls. The model is embedded in computer simulation programs that solve the non‐linear, large deformation equations of compressible solid and fluid flow in space and time. It is implemented as a user‐defined model, which returns the updated stress tensor and composition that result from the simulation supplied strain tensor change. Although it is multi‐phase, in that gas and solid species are present, it is single‐velocity, in that the gas does not flow through the porous solid. More than 70 time‐dependent variables are made available for additional analyses and plotting. The model encompasses a broad range of possible responses: mechanical damage with no energetic response, and a continuous spectrum of degrees of violence including delayed and prompt detonation. This paper describes the basic workings of the model.

“…Ignition occurs because of complex and nonunique causes. For example, frictional heating of high‐melting‐point grit particles is a major cause of ignition during oblique impacts of PBX [2]. Shear behavior induces ignition in typical compression‐shear tests [3].…”

Section: Introductionmentioning

confidence: 99%

Effect of Continuous Damage Accumulation on Ignition of HMX‐Based Polymer Bonded Explosives under Low‐Velocity Impact

Liu

Chen

Zhang

2020

The ignition phenomena of polymer-bonded explosives (PBXs) due to hotspot formation from grit/friction, shear band formation, and friction between microcrack surfaces have not yet been clarified. Microcracks are known to play a critical role in PBX ignition under low-velocity impacts. Further, microcrack evolution determines whether or not a specimen ignites because of complex mechanicalthermal-chemical coupled processes. Although many studies have investigated the multiphysics processes of ignition under single impacts, few have investigated multiple-impact scenarios that are more likely in reality. The present study focuses on the influence of continuous damage accumulation during multiple impacts on the safety assessment of octahydro-1,3,5,7-Tetranitro-Tetrazocine (HMX)-based PBXs. The Visco-SCRAM model combined with restart technology is applied to conduct simulations with the standard confined Steven test. By controlling the first impact velocity, the damage accumulation could be designed. When the first impact velocity increases from 5 to 20 m/s, the second impact velocity threshold decreases from 34 to 22 m/s and specific mechanical energy decreases from 600 to 240 m 2 /s 2. Multiple impacts change the temperature distribution and ignition position. Further, different projectile shapes influence multiple impacts differently. Owing to continuous damage accumulation, the second impact velocity threshold decreases for flat and pin projectiles. Dimensionless analysis reveals that the trends of critical dimensionless parameters for flat and pin projectiles are similar, whereas oval projectiles show a different response.